But whether or not he was feeding on her isn't the point.. He couldn't even touch her without getting burned after Blood Rites. Not sure which book it was or story, but Harry meets them in a bar and is surprised that Thomas has his arm around her, the answer then was a rubber skin suit for her.. Why? When a one night stand with anyone would have solved their problem?
Probably club Zero in TC you're thinking about. Meh, it wasn't enough of a problem to risk Justine's protection. They wouldn't have known for sure that it would have come back before they tested it.
Mostly we have speculation, Aurora is a better example, we all agree for the most part that she was infected by Summer Knight.. But how and who? Speculation, that it was Elaine, but no actual proof or even clues unless you buy she was infected when she fled Justin's house and found refuge at the Summer Court.
Aurora is an exception as a semi-major character where we don't have a good sense of where or when her infection came from. It's hard to give clues about when it happened when she was already infected when Harry met her. If it was Elaine, it'll surely come up when we get to the bottom of her story.
A case can be made that Justine was infected when she was Bianca's prisoner.. Or depending on how far you want to push Nemesis long term planning, she was infected before she got the attention of Lord Raith to be kine for his son, whom he didn't wish well. Or if you buy that Lord Raith has some connection to the Outsiders, we know from White Night that some of them did, he or one of them may have arranged her infestation thinking long term..
He didn't admit to anything, he said...
Nemesis admitted to a vague period of time. He's an Outsider, counting time like a mortal isn't his thing. Could he have been off or lying? Sure, but it's harder to motivate lying to Harry when Nemesis is planning on killing him imminently.
She became close at the end of Blood Rites because Lara felt she owed her for what she did for Thomas. Noe Nemesis could have come out as said that, but he didn't, "mortal time is such a vague concept." What does that mean? Almost everyone here likes the time travel angle to the story, or a time travel angle.. "Mortal time is such a vague concept," means on his time line, not Harry's time line.. In other words, it isn't something that can be pinned down.
Okay, time travel shenanigans could change things. Kinda wrecks the speculation game if you go with the assumption that the words on the page tell you nothing, though. Nemesis answering Harry's question with a general period is Occam's answer.
Yet Justine was busy back stabbing away feeding information to Harry when he needed it.
Are you saying that Justine helping Harry is evidence that Justine was already infected? I don't follow the line of thought here.